i'm sure I have rapped off the pharos in two pitches with a 50 m rope and the watchtower face. I won't promise anything but I don't remember ever dropping my 50m rope over an edge to see the ends dangling any more than a tiny bit above the ground or the next station. My ideal for arapiles would be double 60m ropes (a lot of routes wander a bit) but I really don't think there would be more than a handful of situations that a single 50m wouldn't do the job.
but I agree with others, buy a guide and you'll be fine with your rope.